Excitatory neurotransmitters, the most important of which is glutamate, increase the activity of signal. receiving neurons and play a major role in controlling brain function. Glutamate exerts its effects on cells in part through three types of receptors that, when activated, allow the flow of positively charged ions into the cell. Of these, the N-methyl-D-aspartate (NMDA) receptor plays a particularly important role in controlling the brain's ability to adapt to environmental and genetic influences. Even low alcohol concentrations can inhibit the excitatory activity of the NMDA receptor. This inhibition of NMDA receptor function may be one of the mechanisms contributing to fetal alcohol syndrome and other more subtle developmental abnormalities. Moreover, alcohol-induced impairment of the NMDA receptor may contribute to alcohol-related learning disabilities, neuronal losses, and cognitive deficits as well as to some of the manifestations of alcohol withdrawal.